In a conventional vapor compression refrigeration cycle, a compressor mechanically elevates the temperature and pressure of a working fluid to achieve a desired vapor state. A heat exchanger, designated as a condenser, dissipates heat from the compressed working fluid, thereby condensing the working fluid. An expansion valve or other expansion apparatus lowers the pressure of the working fluid, and the working fluid enters a second heat exchanger, designated as an evaporator, in which heat from the environment to be cooled is absorbed by the working fluid. The now heated working fluid returns to the compressor, and the cycle is repeated. The present invention is directed in part to a novel adaptation of the conventional vapor compression refrigeration cycle.
A vapor compression refrigeration system (xe2x80x9ccooling systemxe2x80x9d) is selected so that its heat removal (or cooling) capacity matches the heat load generated by the space that is to be cooled. The heat load of the space to be cooled will vary according to various factors, including, for example, the season (outdoor temperature), equipment operating within the space, number of people present in the space, etc. Additionally, there are two types of heat that contribute to the heat load. Sensible heat is the heat that produces an increase in temperature of the air in the space to be cooled. Sensible cooling therefore reduces the temperature of the space to be cooled. Latent heat is the heat required to effect a change in the vapor state of the moisture contained in the air of the space to be cooled. Latent cooling therefore reduces the humidity of the space to be cooled.
To provide adequate cooling under all circumstances, the cooling system must have a capacity at least equal to the maximum heat load of the space to be cooled. However, this will result in selection of a cooling system with a capacity larger than required for most operating conditions. If the cooling system is operating at significantly less than its rated capacity, the system will repeatedly cycle on and off, which is undesirable in that it causes undue wear on various cooling system components. This repeated on-off cycling results in short run times which prevent the system from reaching steady-state operation. Conversely, if a cooling system is selected that has a capacity less than the maximum load, under peak load conditions the system will operate continuously. Continuous operation is also undesirable in that it causes undue component wear, increased energy consumption, and fails to provide adequate capacity to maintain the desired environmental conditions. The capacity of the cooling system must be selected to harmonize these two conflicting conditions.
It is therefore desirable to provide a cooling system that provides multiple stages of cooling, i.e., that can accommodate different loads without undesirably short or undesirably long run times. By providing a cooling system comprising multiple cooling circuits having different capacities, it is possible to provide such a multi-stage cooling system. By operating various combinations of the cooling circuits, different cooling capacities may be obtained. It then becomes necessary to determine what designs of condensers, evaporators, and controllers will allow for operation without creating unbalanced loads, compressor overloading, condensate entrainment, undesirably short or undesirably long run times, or other negative side effects.
To address the desire for a cooling system capable of providing a plurality of different cooling capacities, the present invention is directed to an integrated cooling system comprising at least two cooling circuits having independent working fluid circuits under a common control. The present invention is particularly directed to a multi-circuit cooling system in which a first cooling circuit has a different cooling capacity than a second cooling circuit. In accordance with the present invention, it is desirable to provide a condenser having multiple individual condenser coils within a common structure with the coils being arranged in a face-split relation relative to airflow through the condenser, i.e., so that the airstream passes through the individual condenser coils in parallel. Both air-cooled condensers and water-cooled condensers may be used with the present invention. It is also desirable to provide an evaporator having multiple individual evaporator coils within a common structure, with the evaporator coils being arranged in a row-split relation relative to airflow through the condenser, i.e., so that the airstream passes through the first evaporator and second evaporator coil in series.
The present invention is also particularly adapted to providing cooling based on the sensible heat load and latent heat load of the space to be cooled. The control system of the cooling apparatus in accordance with the present invention is therefore adapted to control the individual cooling circuits based on both temperature and humidity. The controller is also adapted to minimize the amount of compressor cycling required to maintain the environment at the desired temperature and humidity.
Although the present invention is disclosed in the context of an integrated cooling system having two cooling circuits under common control, it is to be understood that the invention encompasses cooling systems having any number of cooling circuits. Furthermore, although the detailed design and construction of such systems would be a time-consuming undertaking, it would nonetheless be within the capabilities of one having ordinary skill in the art and the benefit of this disclosure.